This patent application is a companion application of a concurrently filed application directing to a similar subject matter with the title of xe2x80x9cA VARIABLE OPTICAL ATTENUATION COLLIMATORxe2x80x9d by the same inventor.
The present invention relates generally to the field of fiber optical components used in fiber optical communications. More particularity, the present invention discloses a number of concepts for the designing and manufacturing of Variable Optical Attenuation Collimator (VOAC) so as to control the amount of light power propagating through a fiber optical collimator.
The industry of fiber optical communications has already proven to be indispensable for the achievement of low noise, long distance telecommunication with a heretofore-unrealizable high bandwidth. Within a fiber optical network a Variable Optical Attenuator (VOA) is an important basic component with the function of controlling the propagated level of light power, such as a single-channel VOA or a VOA array. The VOA can be combined with other fiber optical components to form modules of a higher level of functionality, such as a Dense Wavelength Division Multiplexer (DWDM), an Optical Add/Drop Multiplexer (OADM) and a Programmable Optical Add/Drop Multiplexer (POADM). For example, in a DWDM, the optical power level of each channel is changed after it passes through Erbium-Doped Fiber optical Amplifiers (EDFAs) and associated fibers. In this case, a VOA is one of the simplest solutions to balancing the optical power level amongst the various wavelengths.
Recently, the need and the art of making the VOA has increased substantially due to the demand of real-time, dynamic light power management within a fiber optical system, especially as the market attention turns from long-haul systems toward metro-systems and even local networks and fiber delivery to individual homes.
However, to date, there has been a general lack of suitable VOA products in the market. For example, to meet the explosively growing traffic demand a high channel-count transmission system will need to accommodate many VOAs in a compact package (the VOA array), which may cause many undesirable effects to the system including, but without limitation to, such problems as pigtail handling and VOA array set-up. To solve such problems commercially, the VOA or VOA array must feature a variety of properties such as small size, consistent and stable attenuation, short response time, very high reliability, easy-to-use while being low cost. Currently, there are three kinds of VOA or VOA array in the market, they are opto-mechanical VOA devices using stepper motor or magneto-optical crystal, VOA arrays based upon waveguide technology and VOAs or VOA arrays based upon MEMS-on-wafer technology where MEMS stands for Micro Electro Mechanical Structure. Unfortunately, none of these existing VOAs or VOA arrays can simultaneously realize all the just-mentioned features. For example, while the opto-mechanical VOAs are capable of providing consistent and stable attenuation by using stepper motor or magneto-optic crystalto drive a shutter or light blocker into a light beam to obstruct part or all of the light power, they can not be minimized to meet the needs of high channel-count integration due to the bulky size of the stepper motor or the electro-magnetic coil. Essentially, the major drawbacks are their bulkiness, long response time, difficulty of system integration and high cost. On the other hand, the waveguide VOAs, while being suitable for high channel-count integration, are lack of consistent and stable attenuation expressed in the form of high insertion loss, high Polarization Dependent Loss (PDL), high Polarization Mode Dispersion (PMD) and sensitivity to ambient temperature. The temperature sensitivity is caused by a differential coefficient of temperature change of the refractive index between the waveguide material and an attached glass fiber core. Additionally, there is difficulty of system integration in the sense that it is difficult to couple light into and out of the ends of the waveguide due to mode difference of the propagating light between the waveguide and an attached fiber. The drawbacks of the MEMS VOA are similar to that of the waveguide VOA. The MEMS VOA usually leaves a narrow air gap between two fiber ends to allow the insertion of a MEMS shutter into the light path. While the MEMS VOA is suitable for assembly into an array by placing the fibers and shutters onto a MEMS wafer, the associated insertion loss, return loss and temperature dependence can not be easily perfected due to the presence of this air gap and the requirement of maintaining parallelism between the end surfaces of the fibers.
The present invention is directed to a number of concepts of designing the Attenuation Control Element (ACE) within the VOAC to perform the function of the aforementioned VOA or VOA arrays while featuring small size, consistent and stable attenuation, short response time, very high reliability, easy-to-use and low cost.
The first objective of this invention is to provide for a VOAC that achieves a consistent and stable attenuation.
The second objective of this invention is to provide for a VOAC that is compact in size.
The third objective of this invention is to provide for a VOAC that achieves a short response time.
The fourth objective of this invention is to provide for a VOAC that is low cost.
Other objectives, together with the foregoing are attained in the exercise of the invention in the following description and resulting in the embodiment illustrated in the accompanying drawings.